Electrode temperature gradients in the electroslag process
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the s l a g / g a s i n t e r f a c e . The study p r e s e n t e d below r e l a t e s to the g r a d i e n t above the s l a g / g a s i n t e r f a c e , and c o m p a r e s e x p e r i m e n t a l r e s u l t s on an ESR unit with a computation of this g r a d i e n t f o r AISI 1018 s t e e l , and 321 s t a i n l e s s s t e e l . EXPERIMENTAL 1) T e m p e r a t u r e M e a s u r e m e n t s The p r o b l e m of t e m p e r a t u r e m e a s u r e m e n t in an o p e r a t i n g ESR unit h a s been studied 2'3 in s e v e r a l cont e x t s . T h e r e e x i s t s s u b s t a n t i a l e x p e r i m e n t a l difficulty in m e a s u r i n g m i l l i v o l t t h e r m o c o u p l e p o t e n t i a l s in a s y s t e m c o n t a i n i n g i n t e n s e m a g n e t i c f i e l d s , at a high t e m p e r a t u r e in a c o r r o s i v e flux and at ac o r dc potent i a l s s i g n i f i c a n t l y above ground. If a b a r e t h e r m o c o u p l e is i m m e r s e d in the flux (which r a p i d l y d i s s o l v e s even c e r m e t r e f r a c t o r i e s ) it will t r a n s i e n t l y r e c o r d the s u r face t e m p e r a t u r e before b e i n g d e s t r o y e d by the m e t a l lic content 4 of the flux. Since the flux is at a potential above ground, the t h e r m o c o u p l e m e a s u r i n g i n s t r u m e n t m u s t be f l o a t i n g and have adequate c o m m o n - m o d e r e j e c t i o n . T r i a l s e s t a b l i s h e d that b o r o n n i t r i d e is an exc e l l e n t m a t e r i a l for t h e r m o c o u p l e p r o t e c t i o n tubes in t h i s context as it is c o m p a t i b l e with the W3Re/W25Re t h e r m o c o u p l e s used, i s an e l e c t r i c a l i n s u l a t o r at the t e m p e r a t u r e s e x p e r i e n c e d , and will r e s i s t attack for a c o n s i d e r a b l e time by ESR f l u x e s u n d e r an a r g o n a t m o s p h e r e . M e a s u r e m e n t s of the flux t e m p e r a t u r e were made with the t h e r m o c o u p l e a s s e m b l y d e s c r i b e d above which was attached to the e l e c t r o d e s u r f a c e and which read out to a S a r g e n t Model SR4 r e c o r d e r . M e a s u r e m e n t s of the t e m p e r a t u r e g r a d i e n t in the e l e c t r o d e were made u s i n g c h r o m e l - a l u m e l t h e r m o c o u p l e s placed in w e l l s {- in. deep d r i l l e d in the e l e c t r o d e in axial sets of f o u r at known i n t e r v a l s . The t h e r m o c o u p l e m e a s u r i n g the flux t e m p e r a t u r e was placed 1 cm ahead of the l e a d i n g e l e c t r o d e t h e r m o c o u p l e , and provided an a c c u r a t e " m a r k e r " of the s l a g / g a s i n t e r f a c e r e l a t i v e to e l e c t r o d e position. Up to twenty s e q u e n c i a l s e t s of four e l e c t r o d e t e m p e r a t u r e g r a d i e n t s were thus obtained for v a r i o u s ESR o p e r a t i n g c o n d i t i o n s . The e l e c t r o d e t h e r m o c o u p l e r e a d - o u t was on a T e x a s I n s t r u m e n t s Mo
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